Measurement - Perimeter of Polygons

Perimeter is the total linear distance around the outside edge of a closed 2D shape. Visually, imagine tracing the boundary of a shape with a pencil; the total length of the line drawn once you return to the start is the perimeter. In diagrams, the perimeter is represented by the sum of all labeled exterior lines.

Units of Measurement: Perimeter is a linear measure, meaning it is expressed in units such as millimeters ($mm$), centimeters ($cm$), meters ($m$), or kilometers ($km$). Visually, check that all side lengths are in the same unit before adding; for example, if one side is in $cm$ and another is in $m$, they must be converted to match.

Regular Polygons are shapes where every side has the same length and every angle is equal. Visually, these are perfectly symmetrical shapes like equilateral triangles or squares. In geometry problems, they are often indicated by a small 'tick mark' on each side to show that every side length is identical.

Irregular Polygons are shapes where side lengths and angles vary. To find the perimeter, you must sum every individual exterior side. Visually, these shapes appear asymmetrical and each side is usually labeled with its specific numerical length because they cannot be assumed to be equal.

Rectangles and Squares: A square has four identical sides, while a rectangle has two pairs of equal opposite sides. Visually, a rectangle's perimeter is the sum of its two lengths ($l$) and its two widths ($w$), covering all four boundary edges: $P = l + w + l + w$.

Composite Figures are complex shapes made by joining two or more simple polygons. The perimeter only includes the outermost edges of the final shape. Visually, any line segments that lie 'inside' the combined shape where the original shapes meet must be ignored as they are no longer part of the boundary.